Diode structures of stacked devices and methods of forming the same

ABSTRACT

Diode structures of stacked devices and methods of forming the same are provided. Diode structures may include a substrate, an upper semiconductor layer that is spaced apart from the substrate in a vertical direction, an upper thin semiconductor layer protruding from a side surface of the upper semiconductor layer in a first horizontal direction, a lower semiconductor layer that is between the substrate and the upper semiconductor layer and has a first conductivity type, a lower thin semiconductor layer protruding from a side surface of the lower semiconductor layer in the first horizontal direction, a first diode contact that is electrically connected to the lower semiconductor layer, and a second diode contact that is electrically connected to one of the upper semiconductor layer and a portion of the substrate. The one of the upper semiconductor layer and the portion of the substrate may have a second conductivity type.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application Ser.No. 63/246,965, entitled DIODE DEVICES FOR 3D STACKED STRUCTURES, filedin the USPTO on Sep. 22, 2021, the disclosure of which is herebyincorporated by reference herein in its entirety.

FIELD

The present disclosure generally relates to the field of electronicsand, more particularly, to integrated circuit devices including stackedtransistors.

BACKGROUND

Integrated circuit devices including stacked transistors, such as acomplementary field effect transistor (CFET) stack, were introduced toreduce their area, thereby increasing the integration density.Integrated circuit devices may also include diodes for variousapplications such as voltage regulation or electrostatic discharge (ESD)protection.

SUMMARY

According to some embodiments of the present invention, diode structuresmay include a substrate, an upper semiconductor layer that is spacedapart from the substrate in a vertical direction, an upper thinsemiconductor layer protruding from a side surface of the uppersemiconductor layer in a first horizontal direction, a lowersemiconductor layer that is between the substrate and the uppersemiconductor layer and has a first conductivity type, a lower thinsemiconductor layer protruding from a side surface of the lowersemiconductor layer in the first horizontal direction, a first diodecontact that is electrically connected to the lower semiconductor layer,and a second diode contact that is electrically connected to one of theupper semiconductor layer and a portion of the substrate. The one of theupper semiconductor layer and the portion of the substrate may have asecond conductivity type.

According to some embodiments of the present invention, integratedcircuit device may include a diode structure. The diode structure mayinclude an upper semiconductor layer on a substrate, an upper thinsemiconductor layer protruding from the upper semiconductor layer, alower semiconductor layer that is between the substrate and the uppersemiconductor layer, a lower thin semiconductor layer protruding fromthe lower semiconductor layer, a first diode contact that iselectrically connected to the lower semiconductor layer or a firstportion of the substrate, and a second diode contact that iselectrically connected to the upper semiconductor layer or a secondportion of the substrate.

According to some embodiments of the present invention, methods offorming an integrated circuit device may include forming a lower thinsemiconductor layer on a substrate, forming a lower semiconductor layercontacting a side surface of the lower thin semiconductor layer, formingan upper thin semiconductor layer, forming an upper semiconductor layercontacting a side surface of the upper thin semiconductor layer, forminga first diode contact that is electrically connected to the lowersemiconductor layer or a first portion of the substrate, and forming asecond diode contact that is electrically connected to the uppersemiconductor layer or a second portion of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an integrated circuit device according to someembodiments of the present invention.

FIGS. 2 and 3 are side views of an integrated circuit device fromviewpoints V and W in FIG. 1 , respectively, according to someembodiments of the present invention.

FIGS. 4 and 5 are cross-sectional views of an integrated circuit devicetaken along the line A-A′ and the line B-B′ in FIG. 1 , respectively,according to some embodiments of the present invention.

FIGS. 6 and 7 are cross-sectional views of an integrated circuit devicetaken along the line A-A′ and the line B-B′ in FIG. 1 , respectively,according to some embodiments of the present invention.

FIGS. 8 and 9 are side views of an integrated circuit device fromviewpoints V and W in FIG. 1 , respectively, according to someembodiments of the present invention.

FIGS. 10 and 11 are side views of an integrated circuit device fromviewpoints V and W in FIG. 1 , respectively, according to someembodiments of the present invention.

FIGS. 12, 13, 14, 15 and 16 are side views of an integrated circuitdevice from viewpoint V in FIG. 1 according to some embodiments of thepresent invention.

FIGS. 17 and 18 are flow charts of methods of forming an integratedcircuit device according to some embodiments of the present invention.

FIGS. 19, 20 and 21 are cross-sectional views taken along the line B-B′and the line C-C′ in FIG. 1 illustrating methods of forming anintegrated circuit device according to some embodiments of the presentinvention.

FIG. 22 is a flow chart of a process of forming diode contacts accordingto some embodiments of the present invention.

FIG. 23 is a cross-sectional view illustrating a process of formingdiode contacts according to some embodiments of the present invention.

DETAILED DESCRIPTION

According to some embodiments of the present invention, diode structuresmay include a vertical diode that includes two semiconductor layersstacked in a vertical direction. The diode structures may be formed byvertical integration. In some embodiments, elements of diode structuresmay be formed concurrently with elements (e.g., an active layer, a gateelectrode, and/or a source/drain region) of stacked transistors ofstandard cells. In some embodiments, diode contacts may be formed byprocesses performed on a front side of a substrate. In some embodiments,at least one of diode contacts may be formed by processes (e.g.,processes of forming a buried power rail (BPR) processes) performed on abackside of a substrate. As used herein the term “and/or” includes anyand all combinations of one or more of the associated listed items.Further, as used herein, “formed concurrently” refers to being formed bythe same fabrication process(es), at approximately (but not necessarilyexactly) the same time.

Diode structures and methods of forming the same pursuant to embodimentsof the present invention can simplify manufacturing processes of anintegrated circuit device that includes both diode structures andstacked transistors, as common manufacturing processes can be used toform both elements of those diodes and elements of the stackedtransistors.

FIG. 1 is a plan view of an integrated circuit device according to someembodiments of the present invention. FIGS. 2 and 3 are side views of anintegrated circuit device 110 from viewpoints V and W in FIG. 1 ,respectively, according to some embodiments of the present invention.FIGS. 4 and 5 are cross-sectional views of the integrated circuit device110 taken along the line A-A′ and the line B-B′ in FIG. 1 ,respectively, according to some embodiments of the present invention.

Referring to FIGS. 1 through 5 , the integrated circuit device 110 mayinclude a stacked transistor structure ST on a substrate 10 and a diodestructure DS. The substrate 10 may include a first surface S1 and asecond surface S2. The first surface S1 and the second surface S2 may beopposite and parallel to each other. The first surface 51 may be a frontside of the substrate 10, and the second surface S2 may be a backside ofthe substrate 10.

The diode structure DS may include a first lower semiconductor layer26L_1 and a second lower semiconductor layer 26L_2 that may be spacedapart from the first lower semiconductor layer 26L_1 in a firstdirection D1. The first direction D1 may be parallel to the firstsurface S1 and the second surface S2 of the substrate 10 and may be afirst horizontal direction. A first lower thin semiconductor layer 22L_1may be provided between the first lower semiconductor layer 26L_1 andthe second lower semiconductor layer 26L_2 and may contact both thefirst lower semiconductor layer 26L_1 and the second lower semiconductorlayer 26L_2. In some embodiments, the first lower thin semiconductorlayer 22L_1 may contact side surfaces of the first lower semiconductorlayer 26L_1 and the second lower semiconductor layer 26L_2 asillustrated in FIG. 5 . The first lower semiconductor layer 26L_1 andthe second lower semiconductor layer 26L_2 may have a first conductivitytype (e.g., an N-type conductivity or a P-type conductivity).

The diode structure DS may also include a first upper semiconductorlayer 26U_1 and a second upper semiconductor layer 26U_2 that may bespaced apart from the first upper semiconductor layer 26U_1 in the firstdirection D1. A first upper thin semiconductor layer 22U_1 may beprovided between the first upper semiconductor layer 26U_1 and thesecond upper semiconductor layer 26U_2 and may contact both the firstupper semiconductor layer 26U_1 and the second upper semiconductor layer26U_2. In some embodiments, the first upper thin semiconductor layer22U_1 may contact side surfaces of the first upper semiconductor layer26U_1 and the second upper semiconductor layer 26U_2 as illustrated inFIG. 5 . The first upper semiconductor layer 26U_1 and the second uppersemiconductor layer 26U_2 may have a second conductivity type that maybe different from the first conductivity type.

The first lower semiconductor layer 26L_1 may contact the first uppersemiconductor layer 26U_1, and the first lower semiconductor layer 26L_1and the first upper semiconductor layer 26U_1 may form a single diode.In some embodiments, an upper surface of the first lower semiconductorlayer 26L_1 may contact a lower surface of the first upper semiconductorlayer 26U_1 as illustrated in FIG. 2 . As used herein, “a lower surfaceof an element A” (or similar language) means a surface of the element Afacing the substrate 10.

A first contact 32_1 that may contact the first lower semiconductorlayer 26L_1 and a second contact 32_2 that may contact the first uppersemiconductor layer 26U_1 may also be provided. The first contact 32_1may contact a side surface of the first lower semiconductor layer 26L_1,and the second contact 32_2 may contact a side surface of the firstupper semiconductor layer 26U_1 as illustrated in FIG. 1 but the presentinvention is not limited thereto. For example, the first contact 32_1may contact an upper surface of the first lower semiconductor layer26L_1, and the second contact 32_2 may contact an upper surface of thefirst upper semiconductor layer 26U_1. The first contact 32_1 and thesecond contact 32_2 may contact portions of the diode, respectively.Accordingly, the first contact 32_1 and the second contact 32_2 may be afirst diode contact and a second diode contact, respectively.

The second lower semiconductor layer 26L_2 may contact the second uppersemiconductor layer 26U_2. In some embodiments, an upper surface of thesecond lower semiconductor layer 26L_2 may contact a lower surface ofthe second upper semiconductor layer 26U_2 as illustrated in FIG. 3 . Afourth contact 32_4 that may contact both the second lower semiconductorlayer 26L_2 and the second upper semiconductor layer 26U_2 may beprovided. In some embodiments, the second lower semiconductor layer26L_2, the second upper semiconductor layer 26U_2 and the fourth contact32_4 may be omitted.

In some embodiments, a first metal layer 24_1 may be provided betweenthe first lower semiconductor layer 26L_1 and the second lowersemiconductor layer 26L_2 and between the first upper semiconductorlayer 26U_1 and the second upper semiconductor layer 26U_2. The firstmetal layer 24_1 may be spaced apart from the first lower semiconductorlayer 26L_1, the second lower semiconductor layer 26L_2, the first uppersemiconductor layer 26U_1 and the second upper semiconductor layer 26U_2as illustrated in FIGS. 1 and 5 . A portion of the first lower thinsemiconductor layer 22L_1 and a portion of the first upper thinsemiconductor layer 22U_1 may be in the first metal layer 24_1 asillustrated in FIGS. 1 and 4 . Although not shown, an insulating layermay be provided between the portion of the first lower thinsemiconductor layer 22L_1 and the first metal layer 24_1 and between theportion of the first upper thin semiconductor layer 22U_1 and the firstmetal layer 24_1.

FIG. 1 illustrates that the stacked transistor structure ST is spacedapart from the diode structure DS in a second direction D2, but thepresent invention is not limited thereto. The second direction D2 may beparallel to the first surface S1 and the second surface S2 of thesubstrate 10 and may be a second horizontal direction. In someembodiments, the stacked transistor structure ST may be spaced apartfrom the diode structure DS in the first direction D1 or in a directionthat may be different from the first direction D1 and the seconddirection D2. The first surface S1 and the second surface S2 of thesubstrate 10 may be spaced apart from each other in a third direction D3that may be perpendicular to the first surface S1 and the second surfaceS2 of the substrate 10 and may be a vertical direction.

Still referring to FIGS. 1 through 5 , the stacked transistor structureST may include a third lower semiconductor layer 26L_3 and a fourthlower semiconductor layer 26L_4 that may be spaced apart from the thirdlower semiconductor layer 26L_3 in the first direction D1. A secondlower thin semiconductor layer 22L_2 may be provided between the thirdlower semiconductor layer 26L_3 and the fourth lower semiconductor layer26L_4 and may contact both the third lower semiconductor layer 26L_3 andthe fourth lower semiconductor layer 26L_4. In some embodiments, thesecond lower thin semiconductor layer 22L_2 may contact side surfaces ofthe third lower semiconductor layer 26L_3 and the fourth lowersemiconductor layer 26L_4. The third lower semiconductor layer 26L_3 andthe fourth lower semiconductor layer 26L_4 may have the firstconductivity type (e.g., an N-type conductivity or a P-typeconductivity). The second lower thin semiconductor layer 22L_2 may be alower active layer of a lower transistor, and the third lowersemiconductor layer 26L_3 and the fourth lower semiconductor layer 26L_4may be lower source/drain regions of the lower transistor.

The stacked transistor structure ST may also include a third uppersemiconductor layer 26U_3 and a fourth upper semiconductor layer 26U_4that may be spaced apart from the third upper semiconductor layer 26U_3in the first direction D1. A second upper thin semiconductor layer 22U_2may be provided between the third upper semiconductor layer 26U_3 andthe fourth upper semiconductor layer 26U_4 and may contact both thethird upper semiconductor layer 26U_3 and the fourth upper semiconductorlayer 26U_4. In some embodiments, the second upper thin semiconductorlayer 22U_2 may contact side surfaces of the third upper semiconductorlayer 26U_3 and the fourth upper semiconductor layer 26U_4. The thirdupper semiconductor layer 26U_3 and the fourth upper semiconductor layer26U_4 may have the second conductivity type. The second upper thinsemiconductor layer 22U_2 may be an upper active layer of an uppertransistor, and the third upper semiconductor layer 26U_3 and the fourthupper semiconductor layer 26U_4 may be upper source/drain regions of theupper transistor.

The third lower semiconductor layer 26L_3 and the third uppersemiconductor layer 26U_3 may be spaced apart from each other in thethird direction D3, and the fourth lower semiconductor layer 26L_4 andthe fourth upper semiconductor layer 26U_4 may be spaced apart from eachother in the third direction D3. The stacked transistor structure ST mayfurther include a fifth contact 32_5, a sixth contact 32_6, an eighthcontact 32_8 and a second metal layer 24_2. The fifth contact 32_5 andthe sixth contact 32_6 may contact the third lower semiconductor layer26L_3 and the third upper semiconductor layer 26U_3, respectively, andthe eighth contact 32_8 may contact both the fourth lower semiconductorlayer 26L_4 and the fourth upper semiconductor layer 26U_4.

The second metal layer 24_2 may be provided between the third lowersemiconductor layer 26L_3 and the fourth lower semiconductor layer 26L_4and between the third upper semiconductor layer 26U_3 and the fourthupper semiconductor layer 26U_4. The second metal layer 24_2 may bespaced apart from the third lower semiconductor layer 26L_3, the fourthlower semiconductor layer 26L_4, the third upper semiconductor layer26U_3 and the fourth upper semiconductor layer 26U_4 as illustrated inFIG. 1 . A portion of the second lower thin semiconductor layer 22L_2and a portion of the second upper thin semiconductor layer 22U_2 may bein the second metal layer 24_2 as illustrated in FIGS. 1 and 4 . Thesecond metal layer 24_2 may be a layer of a gate electrode. Although notshown, an insulating layer (i.e., a gate insulating layer) may beprovided between the portion of the second lower thin semiconductorlayer 22L_2 and the second metal layer 24_2 and between the portion ofthe second upper thin semiconductor layer 22U_2 and the second metallayer 24_2.

In some embodiments, a first upper surface US1 of the first upper thinsemiconductor layer 22U_1 may be coplanar with a second upper surface US2 of the second upper thin semiconductor layer 22U_2, and the firstupper thin semiconductor layer 22U_1 and the second upper thinsemiconductor layer 22U_2 may have an equal thickness in the thirddirection D3 as illustrated in FIG. 4 . In some embodiments, a thirdupper surface US3 of the first lower thin semiconductor layer 22L_1 maybe coplanar with a fourth upper surface US4 of the second lower thinsemiconductor layer 22L_2, and the first lower thin semiconductor layer22L_1 and the second lower thin semiconductor layer 22L_2 may have anequal thickness in the third direction D3 as illustrated in FIG. 4 .

In FIG. 4 , the first upper semiconductor layer 26U_1, the first lowersemiconductor layer 26L_1, the third upper semiconductor layer 26U_3,the third lower semiconductor layer 26L_3 are represented by dottedboxes to show spatial relationships of those with other elements. Insome embodiments, each of the first upper semiconductor layer 26U_1, thefirst lower semiconductor layer 26L_1, the third upper semiconductorlayer 26U_3, and the third lower semiconductor layer 26L_3 may overlapthe entirety of a corresponding thin semiconductor layer in the firstdirection D1 as illustrated in FIG. 4 . For example, the first uppersemiconductor layer 26U_1 may overlap the entirety of the first upperthin semiconductor layer 22U_1. As used herein, “an element Aoverlapping an element B in a direction X” (or similar language) meansthat there is at least one line that extends in the direction X andintersects both the elements A and B.

Although each of the first metal layer 24_1 and the second metal layer24_2 is illustrated in a single layer, the present invention is notlimited thereto. In some embodiments, each of the first metal layer 24_1and the second metal layer 24_2 may include multiple layers. Further, insome embodiments, a lower portion of each of the first metal layer 24_1and the second metal layer 24_2 may include material(s) different froman upper portion of each of the first metal layer 24_1 and the secondmetal layer 24_2. Further, in some embodiments, an isolation layer maybe provided between the lower portion and the upper portion of each ofthe first metal layer 24_1 and the second metal layer 24_2, and thelower portion may be electrically isolated from the upper portion.

The integrated circuit device 110 may further include first to eighthconductive vias 34_1, 34_2, 34_3, 34_4, 34_5, 34_6, 34_7 and 34_8 thatmay contact the first contact 32_1, the second contact 32_2, the firstmetal layer 24_1, the fourth contact 32_4, the fifth contact 32_5, thesixth contact 32_6, the second metal layer 24_2, the eighth contact32_8, respectively. The first to eighth conductive vias 34_1, 34_2,34_3, 34_4, 34_5, 34_6, 34_7 and 34_8 may be electrically connected toconductive wires 36, respectively. In some embodiments, the first toeighth conductive vias 34_1, 34_2, 34_3, 34_4, 34_5, 34_6, 34_7 and 34_8may contact the conductive wires 36, respectively, as illustrated inFIGS. 2 and 3 .

An interlayer insulating layer 42 may be provided on the substrate 10.Although the interlayer insulating layer 42 is illustrated as a singlelayer, the interlayer insulating layer 42 may include multiple layersstacked on the substrate 10. The diode structure DS and the stackedtransistor structure ST may be provided in the interlayer insulatinglayer 42. The interlayer insulating layer 42 may include an insulatingmaterial (e.g., silicon oxide, silicon nitride, silicon oxynitride,silicon carbide and/or low-k material). The low k material may include,for example, fluorine-doped silicon dioxide, organosilicate glass,carbon-doped oxide, porous silicon dioxide, porous organosilicate glass,spin-on organic polymeric dielectrics, or spin-on silicon basedpolymeric dielectric.

The substrate 10 may include one or more semiconductor materials, forexample, Si, Ge, SiGe, GaP, GaAs, SiC, SiGeC and/or InP. In someembodiments, the substrate 10 may be a bulk substrate (e.g., a bulksilicon substrate) or a semiconductor on insulator (SOI) substrate.

Each of the first lower thin semiconductor layer 22L_1, the first upperthin semiconductor layer 22U_1, the second lower thin semiconductorlayer 22L_2 and the second upper thin semiconductor layer 22U_2 mayinclude multiple thin semiconductor layers stacked in the thirddirection D3. For example, the first upper thin semiconductor layer22U_1 may include two thin semiconductor layers as illustrated in FIGS.4 and 5 but the present invention is not limited thereto. Each of thestacked thin semiconductor layers may be a nanosheet. The nanosheet mayinclude semiconductor material(s) (e.g., silicon, germanium,silicon-germanium, and/or III-V semiconductor compound). For example,each of nanosheets may have a thickness in a range of, for example, from1 nm to 100 nm in the third direction D3.

The first and second metal layers 24_1 and 24_2 may include asemiconductor layer (e.g., a poly silicon layer), a work function layer(e.g., TiC layer, TiAl layer, TiAlC layer or TiN layer) and/or a metallayer (e.g., a tungsten layer, an aluminum layer or a copper layer).

Each of the first to fourth lower semiconductor layers 26L_1, 26L_2,26L_3 and 26L_4 and the first to fourth upper semiconductor layers26U_1, 26U_2, 26U_3 and 26U_4 may include semiconductor material(s)(e.g., silicon, germanium, silicon-germanium) and may also includeoptionally dopants (e.g., B, P or As). In some embodiments, the firstlower semiconductor layer 26L_1 and the first upper semiconductor layer26U_1 may be a silicon layer (e.g., an amorphous silicon layer).

The first contact 32_1, the second contact 32_2, the fourth contact32_4, the fifth contact 34_5, the sixth contact 32_6, the eighth contact32_8, the first to eighth conductive vias 34_1, 34_2, 34_3, 34_4, 34_5,34_6, 34_7 and 34_8, and the conductive wires 36 may include a metallayer (e.g., a ruthenium layer, a molybdenum layer, a copper layer, acobalt layer, an aluminum layer and/or a tungsten layer) and/or a metalnitride layer (e.g., a titanium nitride layer and/or a tantalum nitridelayer).

FIGS. 6 and 7 are cross-sectional views of an integrated circuit device120 taken along the line A-A′ and the line B-B′ in FIG. 1 ,respectively, according to some embodiments of the present invention.The integrated circuit device 120 may be similar to the integratedcircuit device 110 with a primary difference being that each of thefirst lower thin semiconductor layer 22L_1, the first upper thinsemiconductor layer 22U_1, the second lower thin semiconductor layer22L_2, the second upper thin semiconductor layer 22U_2 is a single layer(e.g., a single nanosheet).

FIGS. 8 and 9 are side views of an integrated circuit device 130 fromviewpoints V and W in FIG. 1 , respectively, according to someembodiments of the present invention. The integrated circuit device 130may be similar to the integrated circuit device 110 with a primarydifference being that a first intrinsic semiconductor layer 52 isprovided between the first lower semiconductor layer 26L_1 and the firstupper semiconductor layer 26U_1 and contacts both the first lowersemiconductor layer 26L_1 and the first upper semiconductor layer 26U_1.The first lower semiconductor layer 26L_1, the first intrinsicsemiconductor layer 52 and the first upper semiconductor layer 26U_1 maycollectively form a single diode. In some embodiments, the integratedcircuit device 130 may also include a second intrinsic semiconductorlayer 54 that may be provided between the second lower semiconductorlayer 26L_2 and the second upper semiconductor layer 26U_2 and contactsboth the second lower semiconductor layer 26L_2 and the second uppersemiconductor layer 26U_2.

The first intrinsic semiconductor layer 52 and the second intrinsicsemiconductor layer 54 may include silicon and/or silicon germanium andmay have a thickness in a range of 10 nm to 200 nm in the thirddirection D3.

FIGS. 10 and 11 are side views of an integrated circuit device 140 fromviewpoints V and W in FIG. 1 , respectively, according to someembodiments of the present invention. The integrated circuit device 140may be similar to the integrated circuit device 110 with primarydifferences being that the first lower semiconductor layer 26L_1contacts a first portion 62 of the substrate 10. The first lowersemiconductor layer 26L_1 and the first portion 62 of the substrate 10may form a single diode. The first portion 62 of the substrate 10 mayhave the second conductivity type. A ninth contact 32_9 may be providedin the interlayer insulating layer 42 and may contact the first portion62 of the substrate 10. The first contact 32_1 and the ninth contact32_9 may be a first diode contact and a second diode contact,respectively.

The first portion 62 of the substrate 10 may include dopants at aconcentration in a range of 10¹³ cm⁻³ to 10²⁰ cm⁻³. The first portion 62of the substrate 10 may have a thickness in a range of about 10 nm toabout 400 nm (e.g., about 100 nm to about 200 nm) in the third directionD3. The ninth contact 32_9 may include a metal layer (e.g., a rutheniumlayer, a molybdenum layer, a copper layer, a cobalt layer, an aluminumlayer and/or a tungsten layer) and/or a metal nitride layer (e.g., atitanium nitride layer and/or a tantalum nitride layer).

Although FIG. 10 illustrates that the first upper semiconductor layer26U_1 contacts the first lower semiconductor layer 26L_1, in someembodiments, the first upper semiconductor layer 26U_1 may be spacedapart from the first lower semiconductor layer 26L_1 in the thirddirection D3. Further, in some embodiments, the second uppersemiconductor layer 26U_2 may contact the second lower semiconductorlayer 26L_2 as illustrated in FIG. 11 or the second upper semiconductorlayer 26U_2 may be spaced apart from the second lower semiconductorlayer 26L_2 in the third direction D3.

FIG. 12 is a side view of an integrated circuit device 150 fromviewpoint V in FIG. 1 according to some embodiments of the presentinvention. The integrated circuit device 150 may be similar to theintegrated circuit device 140 with primary differences being that athird intrinsic semiconductor layer 56 is provided between the firstportion 62 of the substrate 10 and the first lower semiconductor layer26L_1 and contacts both the first portion 62 of the substrate 10 and thefirst lower semiconductor layer 26L_1. The first lower semiconductorlayer 26L_1, the third intrinsic semiconductor layer 56, and the firstportion 62 of the substrate 10 may collectively form a single diode.

FIG. 13 is a side view of an integrated circuit device 160 fromviewpoint V in FIG. 1 according to some embodiments of the presentinvention. The integrated circuit device 160 may be similar to theintegrated circuit device 140 with a primary difference being that theninth contact 32_9 is in the substrate 10. The ninth contact 32_9includes a surface 32_9S that may be coplanar with the second surface S2of the substrate 10 as illustrated in FIG. 13 . In some embodiments, thesurface 32_9S of the ninth contact 32_9 may protrude outwardly in thethird direction D3 beyond the second surface S2 of the substrate 10 ormay be recessed with respect to the second surface S2 of the substrate10.

FIG. 14 is a side view of an integrated circuit device 170 fromviewpoint V in FIG. 1 according to some embodiments of the presentinvention. The integrated circuit device 170 may be similar to theintegrated circuit device 150 with primary differences being that asecond portion 64 of the substrate 10 and a tenth contact 32_10 may beadditionally provided. The second portion 64 of the substrate 10 mayhave a conductivity type (i.e., the first conductivity type) that isdifferent from the first portion 62 of the substrate 10, and the firstportion 62 and the second portion 64 of the substrate 10 may form asingle diode. The ninth contact 32_9 and the tenth contact 32_10 may bea first diode contact and a second diode contact, respectively.

The second portion 64 of the substrate 10 may include dopants at aconcentration in a range of 10¹³ cm⁻³ to 10²⁰ cm⁻³. The second portion64 of the substrate 10 may have a thickness in a range of about 10 nm toabout 400 nm (e.g., about 100 nm to about 300 nm) in the third directionD3. The tenth contact 32_10 may include a metal layer (e.g., a rutheniumlayer, a molybdenum layer, a copper layer, a cobalt layer, an aluminumlayer and/or a tungsten layer) and/or a metal nitride layer (e.g., atitanium nitride layer and/or a tantalum nitride layer).

FIG. 15 is a side view of an integrated circuit device 180 fromviewpoint V in FIG. 1 according to some embodiments of the presentinvention. The integrated circuit device 180 may be similar to theintegrated circuit device 170 with primary differences being that thefirst lower semiconductor layer 26L_1 is spaced apart from the substrate10 in the third direction D3 and the first upper semiconductor layer26U_1 is spaced apart from the first lower semiconductor layer 26L_1 inthe third direction D3.

FIG. 16 is a side view of an integrated circuit device 190 fromviewpoint V in FIG. 1 according to some embodiments of the presentinvention. The integrated circuit device 190 may be similar to theintegrated circuit device 180 with a primary difference being that thetenth contact 32_10 is in the substrate 10. The tenth contact 32_10includes a surface 32_10S that may be coplanar with the second surfaceS2 of the substrate 10 as illustrated in FIG. 16 . In some embodiments,the surface 32_10S of the tenth contact 32_10 may protrude outwardly inthe third direction D3 beyond the second surface S2 of the substrate 10or may be recessed with respect to the second surface S2 of thesubstrate 10.

FIGS. 17 and 18 are flow charts of methods of forming an integratedcircuit device according to some embodiments of the present invention.FIGS. 19-21 are cross-sectional views taken along the line B-B′ and theline C-C′ in FIG. 1 illustrating methods of forming an integratedcircuit device according to some embodiments of the present invention.Referring to FIG. 17 , the methods may include performing a firstprocess of forming stacked transistors and a diode on a first surface ofa substrate (Block 1000) and performing a second process of formingdiode contacts (Block 2000).

Referring to FIGS. 18 and 19 , the first process of forming stackedtransistors and a diode may include forming a lower thin semiconductorlayer 22L_1 and a lower active layer 22L_2 on a substrate 10 (Block1100). In some embodiments, the lower thin semiconductor layer 22L_1 andthe lower active layer 22L_2 may be formed concurrently at the sameheight from the first surface S1 of the substrate 10. For example, apreliminary lower semiconductor layer may be formed on the substrate 10and then the preliminary lower semiconductor layer may be patterned,thereby forming the lower thin semiconductor layer 22L_1 and the loweractive layer 22L_2. The lower thin semiconductor layer 22L_1 and thelower active layer 22L_2 may be portions of the single preliminary lowersemiconductor layer. A first interlayer insulating layer 42_1 may beformed on the lower thin semiconductor layer 22L_1 and the lower activelayer 22L_2 and may expose opposing side surfaces of the lower thinsemiconductor layer 22L_1 and the lower active layer 22L_2.

Referring to FIGS. 18 and 20 , a lower semiconductor layer (e.g., firstand second lower semiconductor layers 26L_1 and 26L_2) and a lowersource/drain region (e.g., third and fourth lower source/drain regions26L_3 and 26L_4) may be formed (Block 1200). In some embodiments, thefirst and second lower semiconductor layers 26L_1 and 26L_2 may beformed by an epitaxial growth process using the lower thin semiconductorlayer 22L_1 as a seed layer, and the third and fourth lower source/drainregions 26L_3 and 26L_4 may be formed by an epitaxial growth processusing the lower active layer 22L_2 as a seed layer. In some embodiments,the first and second lower semiconductor layers 26L_1 and 26L_2 and thethird and fourth lower source/drain regions 26L_3 and 26L_4 may beformed by a single epitaxial growth process.

Opposing side surfaces of the lower thin semiconductor layer 22L_1 maycontact the first and second lower semiconductor layers 26L_1 and 26L_2,respectively, and opposing side surfaces of the lower active layer 22L_2may contact the third and fourth lower source/drain regions 26L_3 and26L_4, respectively, as illustrated in FIG. 20 .

Referring to FIGS. 18 and 21 , an upper thin semiconductor layer 22U_1and an upper active layer 22U_2 may be formed on the lower thinsemiconductor layer 22L_1 and the lower active layer 22L_2, respectively(Block 1300). A second interlayer insulating layer 42_2 may be formed onthe upper thin semiconductor layer 22U_1 and the upper active layer22U_2 and may expose opposing side surfaces of the upper thinsemiconductor layer 22U_1 and the upper active layer 22U_2.

An upper semiconductor layer (e.g., first and second upper semiconductorlayers 26U_1 and 26U_2) and an upper source/drain region (e.g., thirdand fourth source/drain regions 26U_3 and 26U_4) may be formed (Block1400). In some embodiments, the first and second upper semiconductorlayers 26U_1 and 26U_2 may be formed by an epitaxial growth processusing the upper thin semiconductor layer 22U_1 as a seed layer, and thethird and fourth source/drain regions 26U_3 and 26U_4 may be formed byan epitaxial growth process using the upper active layer 22U_2 as a seedlayer. In some embodiments, the first and second upper semiconductorlayers 26U_1 and 26U_2 and the third and fourth source/drain regions26U_3 and 26U_4 may be formed by a single epitaxial growth process.

Referring to FIGS. 1 to 3 and 18 , the first and second interlayerinsulating layers 42_1 and 42_2 may be removed and a first metal layer24_1 and a second metal layer 24_2 may be formed (Block 1500).

FIG. 22 is a flow chart of the second process of forming diode contactsaccording to some embodiments of the present invention, and FIG. 23 is across-sectional view illustrating the second process. Referring to FIG.22 , the second process may include forming a first diode contact (e.g.,the first contact 32_1 in FIG. 13 or the ninth contact 32_9 in FIG. 16 )(Block 2100), and then performing a thinning process on the secondsurface S2 of the substrate 10 (Block 2200). The thinning process mayinclude an etch process (e.g., a dry etch process and/or a wet etchprocess) and/or a grinding process.

Referring to FIG. 22 , a second diode contact (e.g., the ninth contact32_9 in FIG. 13 or the tenth contact 32_10 in FIG. 16 ) may be formed inthe substrate 10 (Block 2300). Referring to FIG. 23 , the second diodecontact may be formed by etching the second surface S2 of the substrate10 to form an opening 31 and then forming the second diode contact inthe opening 31.

In some embodiments, the second process of forming diode contactsaccording to some embodiments of the present invention may not include athinning process (Block 2200 in FIG. 22 ), and both the first diodecontact (e.g., the first contact 32_1 in FIGS. 2 and 10 or the ninthcontact 32_9 in FIG. 14 ) and the second diode contact (e.g., the secondcontact 32_2 in FIG. 2 , the ninth contact 32_9 in FIG. 10 or the tenthcontact 32_10 in FIG. 14 ) may be formed on the first surface S1 (e.g.,a front side) of the substrate 10 after the first metal layer 24_1 andthe second metal layer 24_2 are formed.

Example embodiments are described herein with reference to theaccompanying drawings. Many different forms and embodiments are possiblewithout deviating from the scope of the present invention. Accordingly,the present invention should not be construed as limited to the exampleembodiments set forth herein. Rather, these example embodiments areprovided so that this disclosure will be thorough and complete and willconvey the scope of the present invention to those skilled in the art.In the drawings, the sizes and relative sizes of layers and regions maybe exaggerated for clarity. Like reference numbers refer to likeelements throughout.

Example embodiments of the present invention are described herein withreference to cross-sectional views that are schematic illustrations ofidealized embodiments and intermediate structures of exampleembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, example embodiments of the present inventionshould not be construed as limited to the particular shapes illustratedherein but include deviations in shapes that result, for example, frommanufacturing, unless the context clearly indicates otherwise.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the present invention belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentinvention. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when used inthis specification, specify the presence of the stated features, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, steps, operations, elements,components and/or groups thereof. As used herein the term “and/or”includes any and all combinations of one or more of the associatedlisted items.

It will be understood that although the terms first, second, etc. may beused herein to describe various elements, these elements should not belimited by these terms. These terms are only used to distinguish oneelement from another. Thus, a first element could be termed a secondelement without departing from the scope of the present invention.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe scope of the invention. Thus, to the maximum extent allowed by law,the scope is to be determined by the broadest permissible interpretationof the following claims and their equivalents and shall not berestricted or limited by the foregoing detailed description.

What is claimed is:
 1. A diode structure comprising: a substrate; anupper semiconductor layer on the substrate, wherein the uppersemiconductor layer is spaced apart from the substrate in a verticaldirection; an upper thin semiconductor layer protruding from a sidesurface of the upper semiconductor layer in a first horizontaldirection; a lower semiconductor layer that is between the substrate andthe upper semiconductor layer and has a first conductivity type; a lowerthin semiconductor layer protruding from a side surface of the lowersemiconductor layer in the first horizontal direction; a first diodecontact that is electrically connected to the lower semiconductor layer;and a second diode contact that is electrically connected to one of theupper semiconductor layer and a portion of the substrate, wherein theone of the upper semiconductor layer and the portion of the substratehas a second conductivity type.
 2. The diode structure of claim 1,wherein the upper semiconductor layer is electrically connected to thesecond diode contact and contacts the lower semiconductor layer.
 3. Thediode structure of claim 1, wherein the upper semiconductor layer iselectrically connected to the second diode contact, and the diodestructure further comprises an intrinsic semiconductor layer that isbetween the lower semiconductor layer and the upper semiconductor layerand contacts both the lower semiconductor layer and the uppersemiconductor layer.
 4. The diode structure of claim 1, wherein theportion of the substrate is electrically connected to the second diodecontact and contacts the portion of the substrate.
 5. The diodestructure of claim 1, wherein the portion of the substrate iselectrically connected to the second diode contact, and the diodestructure further comprises an intrinsic semiconductor layer that isbetween the portion of the substrate and the lower semiconductor layerand contacts both the portion of the substrate and the lowersemiconductor layer.
 6. The diode structure of claim 1, furthercomprising an insulating layer on the substrate, wherein the lowersemiconductor layer and the first diode contact are in the insulatinglayer, and the second diode contact is in the insulating layer or in thesubstrate.
 7. The diode structure of claim 1, wherein one of the lowerthin semiconductor layer and the upper thin semiconductor layercomprises a plurality of thin semiconductor layers that are stacked inthe vertical direction, and the plurality of thin semiconductor layersprotrude from the side surface of the lower semiconductor layer or theupper semiconductor layer in the first horizontal direction.
 8. Thediode structure of claim 1, wherein the lower semiconductor layer is afirst lower semiconductor layer, and the upper semiconductor layer is afirst upper semiconductor layer, the diode structure further comprises asecond upper semiconductor layer and a second lower semiconductor layerthat is between the substrate and the second upper semiconductor layer,the lower thin semiconductor layer contacts both a side surface of thefirst lower semiconductor layer and a side surface of the second lowersemiconductor layer, and the upper thin semiconductor layer contactsboth a side surface of the first upper semiconductor layer and a sidesurface of the second upper semiconductor layer.
 9. The diode structureof claim 1, further comprising a metal layer that is spaced apart fromthe upper semiconductor layer in the first horizontal direction, whereina portion of the upper thin semiconductor layer is in the metal layer.10. The diode structure of claim 1, wherein the upper semiconductorlayer has the second conductivity type and is electrically connected tothe second diode contact, and each of the lower semiconductor layer andthe upper semiconductor layer is a silicon layer.
 11. An integratedcircuit device comprising: a substrate; and a diode structurecomprising: an upper semiconductor layer on the substrate; an upper thinsemiconductor layer protruding from the upper semiconductor layer; alower semiconductor layer that is between the substrate and the uppersemiconductor layer; a lower thin semiconductor layer protruding fromthe lower semiconductor layer; a first diode contact that iselectrically connected to the lower semiconductor layer or a firstportion of the substrate; and a second diode contact that iselectrically connected to the upper semiconductor layer or a secondportion of the substrate.
 12. The integrated circuit device of claim 11further comprising a stacked transistor structure comprising: an uppertransistor comprising an upper active layer that is spaced apart fromthe substrate in a vertical direction; and a lower transistor betweenthe substrate and the upper transistor, the lower transistor comprisinga lower active layer, wherein the upper active layer and the upper thinsemiconductor layer have an equal thickness in the vertical direction,and an uppermost surface of the upper active layer is coplanar with anuppermost surface of the upper thin semiconductor layer.
 13. Theintegrated circuit device of claim 11, wherein the first diode contactis electrically connected to the lower semiconductor layer, and thelower semiconductor layer has a first conductivity type, and the seconddiode contact is electrically connected to the upper semiconductorlayer, and the upper semiconductor layer has a second conductivity type.14. The integrated circuit device of claim 11, wherein the first diodecontact is electrically connected to lower semiconductor layer, and thelower semiconductor layer has a first conductivity type, and the seconddiode contact is electrically connected to the second portion of thesubstrate, and the second portion of the substrate has a secondconductivity type.
 15. The integrated circuit device of claim 11,wherein the first diode contact is electrically connected to the firstportion of the substrate, and the first portion of the substrate has afirst conductivity type, and the second diode contact is electricallyconnected to the second portion of the substrate, and the second portionof the substrate has a second conductivity type.
 16. The integratedcircuit device of claim 15, further comprising an insulating layer onthe substrate, wherein the lower thin semiconductor layer and the firstdiode contact are in the insulating layer, and the second diode contactis in the substrate.
 17. A method of forming an integrated circuitdevice, the method comprising: forming a lower thin semiconductor layeron a substrate; forming a lower semiconductor layer contacting a sidesurface of the lower thin semiconductor layer; forming an upper thinsemiconductor layer; forming an upper semiconductor layer contacting aside surface of the upper thin semiconductor layer; forming a firstdiode contact that is electrically connected to the lower semiconductorlayer or a first portion of the substrate; and forming a second diodecontact that is electrically connected to the upper semiconductor layeror a second portion of the substrate.
 18. The method of claim 17,further comprising forming an intrinsic semiconductor layer that isbetween the lower semiconductor layer and the upper semiconductor layerand contacts both the lower semiconductor layer and the uppersemiconductor layer or is between the substrate and the lowersemiconductor layer and contacts both the substrate and the lowersemiconductor layer.
 19. The method of claim 17, wherein the substratecomprises a first surface facing the lower thin semiconductor layer anda second surface that is opposite and parallel to the first surface ofthe substrate, and the first diode contact is formed by a processperformed on the second surface of the substrate.
 20. The method ofclaim 17, further comprising: forming a lower active layer on thesubstrate; and forming a lower source/drain region contacting a sidesurface of the lower active layer, wherein the lower active layer andthe lower thin semiconductor layer are formed concurrently.